Hazardous waste transportation and disposal

ABSTRACT

An apparatus for holding hazardous waste made up of solids and liquids in a flowable form includes a tank made of material selected to be impervious to and non-corrodible by the hazardous waste and having a non-critical portion, an agitator in the tank having fluid agitation portions oriented for rotational movement about a horizontal axis, a non-sparking motor located within the tank connected to the agitator for imparting rotation to the fluid agitation portions, and a power source for the motor outside the tank having means passing through the non-critical portion of the tank for communicating power from the power source to the motor. Thus, the power source may communicate power to the non-spark generating motor to impart rotation to the agitator to cause the fluid agitation portions to agitate hazardous waste made up of solids and liquids held in the tank to maintain the hazardous waste in flowable form. Preferably, the tank meets United States Department of Transportation Hazardous Waste transport standard MC 307.

This application is a continuation of application Ser. No. 07/622,104,filed Dec. 4, 1990, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for thetransportation of hazardous wastes in which the hazardous waste includesboth solid and liquid components mixed together. The invention providesfor thorough mixing of the solid and liquid components with numerouspertinent advantages.

As people and companies become more and more attuned to the appropriatedisposition of hazardous waste, whether by personal desire or governmentregulation, the need arises for finding suitable ways of handling thesewastes, so that the disposition can be effectuated safely andeconomically.

A particular class of hazardous waste has a high volatility andcombustibility, making it dangerous to handle but useful as a fuel. Anexample of this type of waste is generated by the painting process.Leftover paints, paint thinners, paint solvents, and paint cleaningcompositions are mixed together to yield a mixture which has thesecharacteristics and which is toxic when released to the environment. Anindustry has arisen to use these paint-related wastes as fuel inindustrial burners, most particularly in cement kilns. The kilns burnthe solid and liquid waste as part of the burner fuel, and the ashresidue of the combustion process serves as clinker in the cement. Thehigh temperature in the kiln safely decomposes the various components ofthe paint-related residue to benign discharges. In addition, many of thesolvent components of the waste are recyclable by removal from the wasteby distillation. This reduces the volume of the waste, but increases theproportion of solids.

However, the kilns involved are located at some distance from the originof the waste or the place of distillation, so a need arises to transportthe waste to the kiln. Since the waste is highly combustible,transportation of the waste, by United States Department ofTransportation regulations, must be in tank trucks having specialconstruction. The applicable standard is Department of TransportationHazardous Waste MC 307, which includes requiring that the empty tank notleak when subjected to an air pressure of 1.76 kilograins per squaremeter, so that the structural integrity of the tank must be substantial.Any breach of the wall of the tank requires retesting of the tank to itsMC 307 rating. The entire text of the Department of Transportation MC307 standard is incorporated herein by reference.

At the completion of the trip to the kiln, the discharge of thehazardous waste from the tank to the kiln burner or a holding tank atthe kiln has previously been problematic. The liquid successfully drainsfrom the tank, but a large quantity of the solids remain. Previousattempts to deal with this problem include providing drop centers ordrop bellies in the tanks so that the bottom wall of the tank issloping, and gravity assists in the discharge of solids along with theliquids. This design has met with only limited success.

The retention of solids in the bottom of the tank poses numerousdisadvantages. First, the backhaul of the tank to pick up another loadentails hauling the solids back to the pickup point, making the tankheavier and wasting fuel. Of course, the buildup of the solids reducesthe capacity of the tank so that each subsequent refill of the tankincludes less and less volume. Typically, two inches of solids weredeposited in the bottom of the tank from each load prior to the use ofthe present invention.

Also, the solids have a high BTU level, so that they contribute to thefuel value of the hazardous waste when they are adequately dischargedwith the liquid. For them to remain deposited in the bottom of the tankdiminishes the available fuel value of the waste.

Moreover, the proper operation of the kiln requires the proper mix ofcomponents in the hazardous waste when used a fuel, including maximumallowable levels of chloride and water, and other components. Not onlyare the solids capable of precipitating from the mixture, but some ofthe liquids in the mixture are not entirely miscible. These liquids canseparate, causing the liquid as discharged from the tank to havedifferent fuel values, depending on which portion of the tank is beingdrained at any given time. This can be disruptive to proper operation ofthe kiln or proper complete combustion of the waste so that the kiln'sdischarges fall outside of permissible or desired ranges. As a result,the kiln operator tests each load of waste and sometimes turns away aload found not to meet its specifications.

Some such tests have been erroneous in that only a certain fraction ofthe overall volume of hazardous waste was sampled because of theseparation of components. Although the overall mixture in the tank maybe within the parameters set by the kiln, the precise sample taken bythe kiln tester may fall outside these parameters and result inrejection of the entire truckload.

Typically, the buildup of the solids in the bottom of the tank has beendealt with by having a workman enter the tank with a shovel to shovelthe solids into barrels for processing. Such processing, rather thanbeing a useful disposition of the solids as in burning in the kiln,constitutes underground storage or wasteful incineration. This does not,of course, solve the problems of incomplete mixing of liquids and is nota chore the workman typically enjoys. It is known that a previousattempt to agitate the contents of a hazardous waste transport tankincluded the use of vertically extending augers or the like, but itresulted in a considerable residue of solids in the tank after it wassupposedly drained. While other types of tanks in which agitators areprovided are known, such as concrete mixers and the like, none aredesigned for the hauling of hazardous waste under conditions meetingDepartment of Transportation MC 307 standards.

Thus, the settling of the contents of the tanks has posed numerousproblems, which prior art attempts to rectify have not been successfulin alleviating. Accordingly, there is a need in the art for a method andapparatus for agitating the hazardous waste solids and liquids tomaintain them in flowable form so that they may be fully and usefullydischarged from the tank.

SUMMARY OF THE INVENTION

The present invention fulfills this need in the art by providing anapparatus for holding hazardous waste made up of solids and liquids in aflowable form including a tank made of material selected to beimpervious to and non-corrodible by the hazardous waste and having anon-critical portion, an agitator in the tank having fluid agitationportions oriented for rotational movement about a horizontal axis, anon-sparking motor located within the tank connected to the agitator forimparting rotation to the fluid agitation portions, and a power sourcefor the motor outside the tank having means passing through thenon-critical portion of the tank for communicating power from the powersource to the motor. Thus, the power source may communicate power to thenon-spark generating motor to impart rotation to the agitator to causethe fluid agitation portions to agitate hazardous waste made up ofsolids and liquids held in the tank to maintain the hazardous waste inflowable form.

Preferably, the agitator includes support elements for the fluidagitation portions located completely within the tank, and the supportelements include bronze bearings in which the fluid agitation portionsmay rotate. Desirably, the tank has a central horizontal axis, and thehorizontal axis about which the fluid agitation portions are oriented isparallel and substantially below the central horizontal axis. The fluidagitation portions include an array of axially extending blades. Theblades extend at a slight angle to the axis of rotation so that uponrotation of the blades, the solids component of the hazardous waste istransported axially.

Preferably, the tank meets United States Department of TransportationHazardous Waste transport standard MC 307. The tank is stainless steel,and the agitator is aluminum. The agitator may also be made of stainlesssteel or other suitable material.

In one embodiment, the tank has a rear discharge port and the bladestransport the solids component to the rear discharge port. In anotherembodiment the tank has a drop center discharge port and the agitatorincludes a first set of blades aft of the discharge port and a secondset of blades forward of the discharge port. The blades transport thesolids components to the center discharge port. In this embodiment, thetank may have a forward floor portion slanted rearwardly forward of thedischarge port and an aft floor portion slanted forwardly aft of thedischarge port. Desirably, the first set of blades is oriented forrotation about an axis substantially parallel with the aft floorportion, and the second set of blades is oriented for rotation about anaxis substantially parallel with the forward floor portion.

The non sparking motor may be a hydraulic motor, the power source ahydraulic fluid pump, and the means for communicating power a pair ofhydraulic lines. The non-critical portion of the tank is a manwaycollar, and the hydraulic lines pass through the manway collar.

In one embodiment, the tank is mobile. In this embodiment the apparatusmay include a truck or trailer body on which the tank is mounted.Alternatively, it may include a rail car body or a ship, barge or boaton which the tank is mounted.

In another embodiment (which may also be mobile) the tank has aplurality of compartments, and one of the agitators is located in eachof the compartments. This permits a plurality of mixtures of hazardouswaste to be held in the tank without mixing between the mixtures, butwith each mixture held in a flowable form.

The invention also provides a method of transporting hazardous wastecomposed of solids and liquids including the steps of: depositing thehazardous waste in a United States Department of Transportation MC 307rated tank, moving the tank of hazardous waste to a destination,agitating the hazardous waste to maintain the hazardous waste insubstantially completely flowable form without appreciable solidsdeposition, and discharging the flowable hazardous waste to a suitablerepository. The agitation step includes introducing rotational motion tothe fluid about a horizontal axis. Desirably, but not necessarily, theagitation step occurs simultaneously with the moving step.

The invention also provides a method of maximizing the available fuelvalue of a combustible hazardous waste mixture of solids and liquids,each of the solids and liquids being independently combustible,including the steps of: holding the hazardous waste in a tank, agitatingthe hazardous waste while it is in the tank so that the solids andliquids are in the form of a flowable mixture of independentlycombustible solids and liquids, and discharging the flowable mixture ofindependently combustible solids and liquids from the tank to a burnerfor combustion, whereby both solids and liquids are available to theburner for combustion. In one embodiment this method also includes thestep of providing paint residues, paint thinners, paint cleaningsolvents or the distillation residue thereof as the combustiblehazardous waste. The materials to be hauled may be various, includingfoods, petroleum distillates, oils and other materials.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from a reading of the followingdetailed description of the preferred embodiments along with a study ofthe drawings in which:

FIG. 1 is a side elevation view of apparatus according to one embodimentof the invention, partially broken away and partially shown in schematicform;

FIG. 2 is a schematic sectional view taken along lines 2--2 in FIG. 1and looking in the direction of the arrows;

FIG. 3 is a schematic elevational and sectional view of the invention asembodied in a compartmented rail car;

FIG. 4 is a schematic view of the invention as embodied in a boat; and

FIG. 5 is a sectional view of apparatus according to an embodiment ofthe invention incorporating in a drop center bottom tanker.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to the agitation of hazardous wastesincluding solids and liquids to maintain them in flowable form and willbe described in detail with reference to a particular trailerconfiguration as one embodiment. However, as will be appreciated, theinvention can be used not only in trailers, but also trucks, rail cars(as in FIG. 3), ships, barges and boats (as in FIG. 4) and even instationary tanks. In particular, the latter may be particularly valuablefor a kiln or other installations where the mixture is to be held untilused.

Referring to FIG. 1, a conventional tank trailer has been shown fittedwith the invention. The trailer includes a tank 10, an undercarriagewith wheels 12, and a pin 13. A manway collar 14 provides a hatchwayaccess to the interior of the tank 10 and a rear discharge 15 isprovided, all in conventional fashion. The tank 10 preferably meets thestandards of the United States Department of Transportation Standard MC307 for over-the-road hauling of hazardous waste. As such, it is made of307 stainless steel, or better.

Disposed within the tank 10 is an agitator 20 which includes supports22, shaft 34 and blades 26. The supports 22 can be arranged inside thetank in any suitable fashion, with the supports taking the form of postswelded to the floor of the tank as one suitable embodiment. The shaft 34is arranged to pass through supports 22 in bronze bearings (not shown)and has affixed to it, again by any desired construction, radial arms 24which in turn have axially extending blades 26 affixed thereto.Preferably, the supports, shafts, radial arms and blades are all made ofaluminum to keep the weight of the apparatus as low as possible. In theembodiment shown in FIG. 1, four axially disposed arrays of blades 26are provided, but other arrangements of blades may be substituted. Inparticular, with a central manway collar 14 as shown in FIG. 1, one longset of blades can be mounted fore and another aft of the hydraulic motor28.

In the embodiment depicted in FIG. 1, a single hydraulic motor 28 isprovided driving the shaft 34. In a more preferred embodiment, twohydraulic motors are provided, one driving the forward sets of bladesand the other driving the rearward sets of blades. This permits theblades to be driven in either the same or opposite directions as may bedesired to achieve thorough agitation of the solids and liquids in thetank or to transport the solids and liquids, as will be discussed morelater.

A hydraulic power unit 30 is provided on the outside bottom of the tankand includes a 13 horsepower diesel engine driving a hydraulic pump anda hydraulic fluid reservoir. A hydraulic line 32 extends from thehydraulic pump up the outside of tank 10, sealingly passes through themanway collar 14, and extends down inside the tank 10 to the hydraulicmotor 28. A similar return line 33 is also provided, similarly located.As will be appreciated, the connection through the manway collar 14 ismade to be fluid-tight, but the stresses imposed upon the manway collarare not as great as those on the main body of the tank, so that suchbreach does not compromise the integrity of the tank for purposes ofmeeting the Department of Transportation's MC 307 standard. Thus themanway collar is a non-critical portion of the tank. Other tanks mayhave other non-critical portions.

As can be seen in FIG. 1, the blades are mounted on radial arms 24 so asto clear the bottom of the tank by a comfortable margin, typically aboutan inch. Even with that much clearance, the turbulence caused by therotation of the blades prevents any collection of solids on the bottomof the tank. In addition, the spacing provides for the possibility ofwear on the bronze bearings over time so that the blades 26 cangradually lower towards the floor without interference.

The environment inside the tank is quite harsh, and the components aresubject to wear, particularly the bearings and the seals. Whileexpensive hydraulic motor seals selected for compatibility with themixture to be hauled may be used if desired, it has been found that suchseals are not cost effective. Leakage of hydraulic fluid from the motor28 inside the tank merely causes the discharge of the hydraulic fluidinto the waste material without deleterious effect on either the wastematerial or the hydraulic system. The fluid loss can be easily detectedby loss of fluid from the hydraulic reservoir on the hydraulic powerunit 30, and the fluid lost can be easily and inexpensively replaced.There is no danger of waste material entering or fouling the hydraulicsystem because the pressure difference between the hydraulic line andthe waste material prevents passage of waste material into the hydraulicsystem.

As can be seen in FIG. 2, the blades 26 are inclined to the shaft 34 ata slight angle, typically about 6 degrees. That is, the sets of radialarms 24 are rotate with respect to fore and aft sets of radial arms sothat the affixation of the blades 26 top the arms 24 inclines the blades26. The effect of the angle of the blade is to impart a slight axial aswell as rotational motion to the solids, so that the solids aretransported axially. This feature can be used to advantage to transportthe solids toward the discharge 15 of the tank.

The location of the discharge port on a given tank may indicate the mostadvantageous arrangement of blades and their angles. The hydraulic motor28 is typically operable in either direction by reversal of thehydraulic fluid pressure in lines 32,33 so that the axial transport ofsolids can be reversed if desired. As can be appreciated from eitherdrawing figure, the shaft 34 forming the axis of rotation of theagitator is at a level below the axis of the entire tank. This has beenfound to provide very good mixing in that the solids and liquids are notonly brought up from the bottom of the tank, but sheared into the upperlayers, which are, in turn, pulled down by the downward motion of theblades on their return paths.

The mounting of the apparatus including supports, shaft, agitator andmotor all entirely within the tank 10 means that there are no breachesin the structural integrity of the tank 10 other than the unimportantentrances of the hydraulic line through the manway collar 10. Thisensures that leakage of the hazardous waste through a failed bearing orseal cannot take place.

In operation, the tank 10 is loaded with the solids and liquid mixturethrough the manway collar 14. The tank sets off for its destination withthe hydraulic power unit 30 turned on, providing hydraulic fluid underpressure through hydraulic lines 32,33 to drive hydraulic motor 28 andthereby rotate the agitator 20.

As the tank is taken to the kiln, the rotation of the blades 26gradually causes the solids accumulation to increase towards the rear ofthe tank, although the entire solids and liquid mixture is kept in aflowable form without appreciable deposit on the floor of tank 10. Uponarrival at the kiln, the tank can remain parked for an extended periodof time with the solids and liquids maintained in a flowable form bycontinued operation of the agitator. This can be helpful if the truckmust wait its turn to unload. Then the tank 10 is connected to theburner intake through its rear discharge 15 in conventional fashion,while the agitator 20 continues to run. The tank is completely drainedof solids and liquids passing through the discharge 15. If desired, thetank can be pressurized with air pressure applied through manway collar14 or another fitting to speed up the discharge, but that is notnecessary.

Alternatively, the solids and liquids can be deposited into the tankwithout the agitator in operation, and the solids can be allowed tosettle to the bottom. Then, the agitator can be started so the solidsand liquids mixture will be fluidized for discharge. If the solidscontents is great, it may be necessary to waggle the agitator to and froto loosen the solids to permit full rotation to begin. Continuedrotation thereafter will maintain the solids and liquids in flowableform.

The apparatus may be installed in level center discharge, drop center ordrop belly tanks known to the art. An example of a drop body tank with adrop center discharge port 315 in tank bottom 317 is illustrated in FIG.5. This will assist in assuring movement of the solids and liquids tothe center discharge. Preferably, in such a tank, agitators are providedfore and aft of the discharge port. Each is rotatable about an axis ofrotation parallel with the floor of the portion of the tank in which theagitator is installed. Thus, the axes of rotation will not be parallelto one another.

In addition, agitators can be provided in known compartmented tanks sothat each compartment receives its own mixture and is maintained in aflowable state. This can be seen in the embodiment depicted in FIG. 3 inwhich the invention is installed in a compartmented rail car. Eachcompartment 110, 111, 112 is supplied with its own manway collar,agitator 120 and discharge port. A single hydraulic pump 130 may beprovided, along with control valves (not shown) suitable for selectivelyoperating the agitators as desired.

In the embodiment of FIG. 4, the tank 210 is provided with an agitator220 tapered to conform to the boat hull. The other components includinga non-sparking motor and power supply therefor 230 are provided,analogously to those described with reference to FIG. 1.

The thorough mixing that the solids and liquids are given by the presentinvention not only assures that the tank will be completely drained whendesired, but the usefulness of the hazardous waste as a combustible fuelis increased in several ways. First, the effective fuel value of thewaste is increased because of the higher BTU content of the solids thanthe liquids. Since the solids are being more completely discharged andused as the fuel, the effective BTU rating of the fuel increases.Furthermore, since the solids and liquids are mixed together, the liquidwhen used as a fuel is more homogeneous, so it gives more consistentburning properties and results in more uniform ash, which is distributedin the cement as clinker. Finally, when the kiln operator samples thewaste to test it, a more accurate reading of the components of the wasteis obtained since it is a more homogeneous mixture. That is, componentshave not separated from one another by settling. The owner of the tankgets full use of his or her tank when equipped with the apparatus of thepresent invention since the finite volume of the tank does not diminishwith time due to the buildup of solids. Also, in a mobile tank, the fuelconsumption of the truck, tractor or the like on the backhaul is reducedsince no dead load is carried.

But perhaps the most important contribution of this invention is the waythat it permits the solids to be used as useful fuel, rather than beingburied for posterity or being burned in a waste incinerator where thefuel value is minimal. Last but not least, the worker who's no longerasked to enter a tank to shovel this solid material appreciates thisinvention, too.

Although the invention lids been described with respect to specificembodiments, various other applications of the invention will come tothose of ordinary skill in the art, and the invention should not bedeemed to be limited to the embodiments described herein.

What is claimed is:
 1. An apparatus for containing a load of hazardoussubstances including liquids and solids, a top surface of the loaddefining a load level, the apparatus comprising:a closed tank forcontaining the load of hazardous substances and including a tank bottomand opposing side walls, said tank having a top portion, a manholeopening located in the top portion, and a valved opening located in thebottom agitating means located in the tank and extending between theside walls for agitating substances within the tank to prevent thesolids from settling on the bottom of the tank, the agitating meansincluding a shaft rotatably mounted in the tank, extending substantiallyparallel to the tank bottom and having first and second distal shaftends, said side walls of the tank being imperforate in areas adjacentthe first and second distal shaft ends; means located in said tank forsupporting said shaft such that the entire agitating means, includingthe first and second distal shaft ends, is completely contained andsupported within the interior of the tank; a non-sparking motor forrotating the shaft, the motor being located within the tank beneath theload level and being submerged in at least a portion of the hazardoussubstances when the tank is loaded; and means for transmitting power tothe non-sparking motor.
 2. An apparatus as claimed in claim 1 whereinsaid means for supporting includes support elements located within thetank, the support elements for engaging the shaft.
 3. An apparatus asclaimed in claim 2 wherein said support elements include bronze bearingsin which said shaft may rotate.
 4. An apparatus as claimed in claim 1wherein said tank has a central horizontal axis, the shaft being locatedparallel to and substantially below said central horizontal axis.
 5. Anapparatus as claimed in claim 1 wherein said tank is stainless steel andsaid agitating means include aluminum.
 6. An apparatus as claimed inclaim 1 wherein said agitating means includes an array of blades and theshaft includes a substantially horizontal axis, the blades extendingsubstantially parallel to the horizontal axis of the shaft.
 7. Anapparatus as claimed in claim 6 wherein said tank has a rear dischargeport and said blades transport the solids component to said reardischarge port.
 8. An apparatus as claimed in claim 1 wherein said tankhas a drop center discharge port and said agitating means includes afirst set of blades aft of said discharge port and a second set ofblades forward of said discharge port, said blades for transportinghazardous waste to said center discharge port.
 9. An apparatus asclaimed in claim 8 wherein said tank has a forward floor portion locatedforward of said discharge port and slanted rearwardly, and an aft floorportion located aft of said discharge port and slanted forwardly.
 10. Anapparatus as claimed in claim 9 wherein said first set of blades isoriented for rotation about an axis substantially parallel to the aftfloor portion and said second set of blades is oriented for rotationabout an axis substantially parallel to the forward floor portion. 11.An apparatus as claimed in claim 1 wherein said non-sparking motor is ahydraulic motor and said means for transmitting power includes ahydraulic fluid pump and a pair of hydraulic lines, the hydraulic linesconnecting the pump to the motor.
 12. An apparatus as claimed in claim11 wherein the manhole opening includes a manway collar and saidhydraulic lines pass through said manway collar.
 13. An apparatus asclaimed in claim 1 wherein said tank is mobile.
 14. An apparatus asclaimed in claim 13 further comprising a truck or trailer body on whichsaid tank is mounted.
 15. An apparatus as claimed in claim 13 furthercomprising a rail car body on which said tank is mounted.
 16. Anapparatus as claimed in claim 13 further comprising a ship or boat onwhich said tank is mounted.
 17. An apparatus as claimed in claim 1wherein the tank includes a plurality of isolated compartments and theagitating means includes a plurality of agitators one of said agitatorsbeing located in each of said compartments.
 18. An apparatus as claimedin claim 1 wherein the shaft extends substantially along an entirelength of the tank bottom.
 19. An apparatus for transporting a hazardoussubstance, the apparatus comprising:an elongated closed tank having atubular outer wall with opposing distal ends, said tank having a bottomportion and a top portion, a manhole opening located in the top portion,and a valved opening located in the bottom portion; a pair of opposingimperforate side walls, each side wall being located on an opposingdistal end of the tubular tank wall; elongated agitation means mountedwithin the tank and extending substantially along the entire length ofthe elongated tank between the side walls for agitating substanceswithin the tank, said elongated agitation means having first and seconddistal ends; means located within the tank for supporting said agitationmeans, each of the distal ends of the agitation means being spaced froman adjacent side wall of the tank such that the entire agitation means,including the first and second distal ends, is completely contained andsupported within the interior of the tank; a non-sparking motor forrotating the agitation means, the motor being located within the tankand being submerged in the hazardous substance when the tank is loaded;and means for transmitting power to the non-sparking motor.